Cholesterol and phytosterols are very similar in molecular structure and are found in animal and plant cellular membranes, respectively. Both chemical species serve as membrane structural elements and also serve functional roles in living cells. These roles include affecting signal transduction, protein and enzyme binding, membrane elasticity, and a variety of other functions. Cholesterol crystallization has been implicated in pathological conditions ranging from gallstone formation to arterial plaque and lesion formation. Maintaining cholesterol in a soluble or semi-soluble state, rather than a crystalline state, within the cell membrane is important. It remains unclear exactly how this is accomplished within the complexity of a living cell's membrane; however, cholesterol combines with phosphatidylcholine, a phospholipid, which seems to maintain cholesterol solubility. Nevertheless, there are limits to the amount of cholesterol that can be combined with such a phospholipid, beyond which the cholesterol precipitates in crystalline form.
While preventing cholesterol crystallization has health implications and has been the subject of a large number of research studies, the prevention of phytosterol crystallization has been less well studied, since the latter does not relate to a pathological state in humans. However, converting phytosterols from their inherently crystalline state to a soluble or dispersed state, and in a micron-sized or submicron-sized microparticulate form, increases their biological efficacy, which is chiefly to facilitate fecal elimination of cholesterol by admixing with cholesterol in the GI tract. To this end, phytosterols have been combined with a variety of edible solvents, co-solvents, emulsifiers and the like.
Phytosterols including beta-sitosterol, campesterol, stigmasterol and brassicasterol are natural, edible, hydrophobic substances that are commercially isolated from vegetable oils and tall oils. When ingested, these substances mix with dietary and endogenously synthesized cholesterol, and can reduce the amount of cholesterol absorbed into the bloodstream to varying degrees. Like cholesterol, the phytosterols readily crystallize in a variety of morphologies (e.g., needles, plates and rods), all of which are poorly dispersible in water. Compositions and methods have been described which are intended to increase the efficacy of phytosterols in eliminating cholesterol from the gastrointestinal tract. For example, emulsifiers have been used to facilitate the dispersal of non-solubilized phytosterols. One such system is described by Traska et al. in U.S. Pat. No. 6,423,363, which discloses processed foods having an aqueous phase dispersion containing a high melting lipid, such as a phytosterol, that is emulsified with a non-sterol emulsifier. However, dispersions produced from phytosterols and non-sterol emulsifiers that are melting together as described by Traska et al. and dispersed by shear in water typically contain relatively large microparticles (e.g., 10-15 microns). This substantial size that can limit the bioavailability of phytosterols in binding and eliminating cholesterol in the GI tract, as well as the ability to maintain stable suspensions in beverages and other useful compositions. The large size appears to be attributable to the crystalline structure maintained in phytosterol-emulsifier mixed solids formed during cooling of molten mixtures described by Traska et al.
There remains a need to develop compositions that more fully and stably disperse phytosterols in aqueous media for use in food and beverage compositions.